In addition to simply run your application, Google App Engine provides full suite of features to manage and operate:

Traffic Splitting - Deploy multiple versions of your application and split traffic to different versions. This is also great for canary new changes.

Stackdriver Logging - Automatically capture and store application logs in centralized logging that can be searched, monitored, and exported.

Error Reporting - Automatically extract errors and exceptions for the log and notify you of new errors.

Cloud Debugger - Allow you to debug your production application without stopping the world. If you needed more log messages to diagnose the issue, simply add new log messages without redeploying/restarting your application.